Preferential infection of dividing cells by Cryptosporidium parvum.

In spite of its limitations, the culture of Cryptosporidium parvum in monolayers of epithelial cells is a suitable model to study the interaction of this protozoan parasite with the host cell, to assay oocyst infectivity, and to screen drugs for anti-cryptosporidial activity. For unknown reasons, growth of Cryptosporidium in culture is limited in time and generally does not lead to the production of significant numbers of oocysts. In monolayers infected with high doses of oocysts, we observed that many cells remain uninfected, suggesting that some cells are less susceptible to the infection. Since C. parvum and the related species C. hominis lack many essential biosynthetic pathways, we tested whether the dependence of the parasite on host cell metabolites may favour the infection of cells in mitosis. The proportion of monolayer cells in stationary (G0/G1) phase and in mitosis (S/G2/M) was determined and the prevalence of infected cells in each subpopulation was quantified. Although C. parvum infects and develops in dividing and stationary cells, a significant preference for cells in S/G2/M phase was observed. Consistent with previous observations showing that C. parvum induces apoptosis in cell monolayers, infection was accompanied by a significant increase in the proportion of mitotic cells.